[daala] Fixing problem with shadowed variables

[Timothy B. Terriberry]

Danesh Daroui wrote:
> -          unsigned w;
> +          unsigned local_w;

I would recommend using a (slightly) less confusing name like "window". 
You should also change the corresponding lines in the horizontal loop 
above, e.g.,

           w=hkernel[k];

etc. Since the code is meant to follow the same pattern in both places, 
it would be helpful if it used the same variable names.